US20170087610A1

US20170087610A1 - Thermoplastic forming of cold rolled alloys

Info

Publication number: US20170087610A1
Application number: US15/258,724
Authority: US
Inventors: Yoshihiko Yokoyama; Theodore A. Waniuk; Hsiang Hung Chen; Kazuya Takagi; Naoto Matsuyuki
Original assignee: Apple Inc
Current assignee: Apple Inc
Priority date: 2015-09-30
Filing date: 2016-09-07
Publication date: 2017-03-30

Abstract

The disclosure is directed to methods of forming glassy alloys. A glassy alloy is cold rolled at a temperature less than Tg of the glassy alloy to form a flattened glassy alloy. Then, the cold rolled glassy alloy is thermoplastically formed at a temperature above Tg of the glassy alloy. In certain embodiments, the flattened glassy alloy may have one or more shear bands and/or micro-cracks, and the thermoplastic forming may heal the shear bands and/or micro-cracks. The resulting glassy alloy may thereby have reduced or eliminated shear bands and/or micro-cracks.

Description

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This patent application claims the benefit under 35 U.S.C. §119(e) of U.S. Patent Application No. 62/234,743, entitled “THERMOPLASTIC FORMING OF COLD ROLLED ALLOYS,” filed on Sep. 30, 2015, which is incorporated herein by reference in its entirety.

FIELD

The disclosure relates generally to methods for forming of glassy alloys. More particularly, the disclosure relates to methods of cold rolling, then for thermoplastic forming, glassy alloys.

BACKGROUND

Glassy alloys (also referred to herein as amorphous alloys or metallic glasses) are alloys that do not have a crystalline structure. Instead, glassy alloys are amorphous. Glassy alloys have a number of beneficial material properties that make them viable for use in a number of engineering applications.
Various methods have been used to process glassy alloys in an attempt to produce glassy alloy parts. However, viscosities of glassy alloys are typically above 10⁵Pas. As such, many traditional methods of processing alloys lead to the formation of shear bands and/or micro-cracks. For instance, methods of cold rolling glassy alloys cause shear band formation (i.e. inhomogeneous deformation) and/or formation of micro-cracks. High viscosities (10⁵-10⁷Pas) in the supercooled liquid region also create difficulties for the precise formation of amorphous metal parts from amorphous alloy feedstock using thermoplastic forming techniques. Neither technique has been considered viable for manufacturing or forming glassy alloys.
Precise glassy alloy parts cannot ordinarily be produced using either method. As a result, glassy alloys can be difficult to form into parts with predictable thicknesses and shapes for use in commercial products. The present disclosure addresses these and other limitations.

SUMMARY

In certain aspects, the disclosure is directed to methods of forming a glassy alloys and glassy alloy parts by thermoplastically forming a cold rolled glassy alloy feedstock.
In certain embodiments, a glassy alloy feedstock is cold rolled at a temperature less than Tg (the glass transition temperature) of the glassy alloy feedstock to form a flattened glassy alloy. The flattened glassy alloy may then be thermoplastically formed at a temperature at or above Tg of the glassy alloy feedstock, e.g., to form a glassy alloy part.
In certain embodiments, the cold rolled, flattened glassy alloy may have one or more shear bands. In certain embodiments, the thermoplastic forming may be used to heal one or more shear bands in the cold rolled, flattened glassy alloy to form a substantially shear band-free glassy alloy.
In certain embodiments, the thermoplastic forming may be used to form glassy alloy parts with desired properties, such as desired three-dimensional shapes, desired thickness, desired bending stress, etc.
In certain aspects, the glassy alloy part may be comprised of a glassy alloy and formed from a combination of cold rolling and thermoplastic forming, wherein the glassy alloy part has a variation in thickness of less than about 10% and is substantially free of shear bands.
In another aspect, the disclosure is directed to methods of determining the presence of crystalline metal in a glassy alloy. First, the glassy alloy feedstock is cold rolled at a temperature less than Tg of the glassy alloy to form a flattened glassy alloy. The presence of cracks radiating from a portion of the alloy corresponds to the presence of a crystalline metal.
Additional embodiments and features are set forth in part in the description that follows, and will become apparent to those skilled in the art upon reading of the specification. A further understanding of the nature and advantages of the present disclosure can be realized by reference to the remaining portions of the specification and the drawings, which forms a part of this disclosure.

BRIEF DESCRIPTION OF THE FIGURES

Although the following figures and description illustrate specific embodiments and examples, the skilled artisan will appreciate that various changes and modifications may be made without departing from the spirit and scope of the disclosure.

FIG. 1A depicts side view of as-cast rectangular shaped glassy alloy having a thickness of about 2 mm.

FIG. 1B depicts side view of a few percent cold rolled glassy alloy.

FIG. 1C depicts side view of 90% cold rolled glassy alloy.

FIG. 2 depicts a temperature-viscosity diagram of an exemplary bulk solidifying metallic glass alloy.

FIG. 3 depicts a schematic of a time-temperature-transformation (TTT) diagram for an exemplary bulk solidifying metallic glass alloy.

FIG. 4A depicts a graph of plate thickness vs. thickness of thermoplastic forming for four glassy alloy samples.

FIG. 4B depicts a thermoplastic pressed plate having variable thickness throughout.

FIG. 4C depicts cold rolled ribbon of glassy alloy having reproducible thickness.

FIG. 5 shows the bending deflection curves of as-cast glassy alloys compared to cold rolled/thermoplastic formed Pt850 alloys in a 3-points bending test.

FIG. 6A shows the cross-section of a punched glassy alloy prepared by cold-rolling and thermoplastic forming.

FIG. 6B depicts an exploded view and lack of undercut resulting from punching the glassy alloy of FIG. 6A.

FIG. 6C depicts an exploded view and lack of burr resulting from punching the glassy alloy of FIG. 6A.

DETAILED DESCRIPTION

Reference will now be made in detail to representative embodiments described herein and illustrated in the accompanying drawings. It should be understood that the following descriptions are not intended to limit the embodiments to one preferred embodiment. To the contrary, it is intended to cover alternatives, modifications, and equivalents as can be included within the spirit and scope of the described embodiments as defined by the appended claims.
In various aspects of the disclosure, cold rolled and thermoplastically formed glassy alloys and glassy alloy parts can be formed with higher precision and desired properties. In some embodiments, cold rolling of glassy alloy feedstock provides heightened thickness control, while thermoplastic forming heals shear bands and/or micro-cracks formed during cold rolling of the glassy alloy feedstock. In some embodiments, the resulting glassy alloys can have increased strength.
In certain aspects, the disclosure is directed to methods of forming glassy alloys and glassy alloy parts by thermoplastically forming a cold rolled glassy alloy feedstock. In certain embodiments, a glassy alloy feedstock is cold rolled at a temperature less than Tg (the glass transition temperature) of the glassy alloy feedstock to form a flattened glassy alloy. The flattened glassy alloy may then be thermoplastically formed at a temperature at or above Tg of the glassy alloy feedstock, e.g., to form a glassy alloy or glassy alloy part. In certain embodiments, the cold rolled, flattened glassy alloy may have one or more shear bands. In certain embodiments, the thermoplastic forming may be used to heal one or more shear bands in the cold rolled, flattened glassy alloy to form a substantially shear band-free glassy alloy.
In certain aspects of the disclosure, the combination of cold rolling and thermoplastic forming provides for control of part thickness, reproducibility, absence of shear bands and/or micro-cracks, and/or retention of metallic glass properties. For instance, in certain embodiments, the methods of the disclosure may be used to form glassy alloy and glassy alloy parts with desired properties, such as desired three-dimensional shapes, desired thickness, desired bending stress, etc. In various aspects, the formed glassy alloy and glassy alloy parts may have, e.g., a consistent thickness, reduced or eliminated shear bands and/or micro-cracks. In certain embodiments, the present disclosure provides for formation of glassy alloy parts without casting or injection molding.
In certain aspects, methods of forming glassy alloys and glassy alloy parts using a combination of cold rolling and thermoplastic forming are provided. In accordance with the disclosure, the combination of cold rolling and thermoplastic forming processes can improve structural integrity of glassy alloys and glassy alloy parts, as well as reduce or eliminate associated cosmetic defects such as shear bands and/or micro-cracks. As described herein, the glassy alloy and glassy alloy parts can be substantially shear band-free. As used herein, substantially shear band-free glassy alloy can have less than 2% of the total surface area of the glassy alloy having shear bands. Alternatively, substantially shear band-free glassy alloy can have less than 1% of the total surface area of the glassy alloy having shear bands. Alternatively, substantially shear band-free glassy alloy can have less than 0.1% of the total surface area of the glassy alloy having shear bands. Alternatively, substantially shear band-free glassy alloy can have less than 0.01% of the total surface area of the glassy alloy having shear bands. Alternatively, substantially shear band-free glassy alloy can have no shear bands.
Any suitable cold rolling method and apparatus/mill known in the art may be used in connection with the present disclosure. As understood by those of skill in the art, in accordance with aspects of the disclosure cold rolling is performed at temperatures below Tg of the glass metal feedstock. In certain aspects, pressure is controlled to obtain and maintain the desired thickness tolerance, as discussed in further detail herein.
Cold rolling at a temperature below Tg allows glassy alloys to be processed to have a predictable and precise thickness. Without wishing to be limited to any particular theory or mode of action, shear bands and micro-cracks can form when the glassy alloy is cold rolled due to the stress imparted on the alloy. FIG. 1A depicts side view of as-cast rectangular shaped glassy alloy having a thickness of about 2 mm. FIG. 1B shows roughly parallel shear bands 106 running throughout cold rolled glassy alloy 102. Initial shear bands were introduced to the glassy alloy. The thickness of the glassy alloy feedstock was reduced by tilting the shear bands under cold rolling up to about 30% at the critical point to introduce second shear bands. A large number of fine and coarse density shear bands were observed. FIG. 1C depicts a side view of 90% cold rolled glassy alloy showing a micro-crack (open gap of shear band) 104 formed at the rolled surface of 90% cold rolled glassy alloy 102. The thickness of the cold rolled glassy alloy had an accurate and reproducible thickness of about 200 μm.
In accordance with certain aspects, any suitable thermoforming technique known in the art may be used in connection with the present disclosure. As understood by those of skill in the art, in accordance with methods described herein, during thermoplastic forming, the flattened, cold rolled glassy alloy is thermoplastically formed at a temperature above the Tg of the glassy alloy feedstock, during which there is a substantial drop in viscosity. As will be recognized by those skilled in the art, different glassy alloys can be thermoplastically formed for different periods of time. In certain variations, the period of time can be 15 seconds, 30 seconds, 45 seconds, 60 seconds, 75 seconds, or 90 seconds. The amount of time can depend on the glassy alloy.
In certain embodiments, the combination of cold rolling and thermoplastic forming provides thickness control. Cold rolling of glassy alloys alone results in shear bands and/or micro-cracks. Thermoplastic forming of glassy alloys alone does not result in predictable or controllable thicknesses. In certain embodiments, the combination of cold rolling and thermoplastic forming described herein controls thickness variation (i.e., variation within a single alloy piece/part and variation between production runs) to within less than about 10%, less than about 8%, less than about 6%, less than about 5%, etc. Predictable thickness is particularly important in glassy alloys that have mechanical properties that depend on thickness (e.g., leaf springs). The combination of cold rolling and thermoplastic forming results in predictable and reproducible formation of glassy alloy thicknesses, and further materials that have the benefit of glassy alloys. Without wishing to be limited to a theory or specific mode of action, cold rolling provides thickness control, and thermoplastic forming provides shape control, of the resulting metallic glass.
In certain embodiments, the glassy alloys and glassy alloy parts of the disclosure can be formed with a predictable and reproducible shape and thickness using the methods described herein. In certain embodiments, cold rolling of a glassy alloy feedstock can provide control of the thickness of a flattened, cold rolled glassy alloy for use in thermoplastic forming to within a desired tolerance of, e.g., within about 0.1 mm, about 0.08 mm, about 0.06 mm, about 0.05 mm, about 0.04 mm, about 0.03 mm, etc., of the final thickness of the processed thermoplastic formed glassy alloy. The thickness of a thermoplastically formed glassy alloy or glassy alloy part using such a flattened, cold rolled glassy alloy can thereby be formed with high precision. In addition, by first cold rolling a glassy alloy and then thermoplastically forming the cold rolled glassy alloy, the time and load for thermoplastic forming can be reduced.
Surprisingly, glassy alloys that are cold rolled and then thermoplastically formed as described herein do not become brittle, and in some instances can become stronger while shear bands relax and micro-cracks diminish. Again without wishing to be limited to a particular mechanism or mode of action, glassy alloy atoms heated above the Tg of the glassy alloy relax. In most glassy alloys, this results in embrittlement and loss of properties such as strength. If the glassy alloy is thermoplastically formed for a certain period of time (e.g., 15 s to 90 s), the lack of embrittlement can also be accompanied by increased strength.
The cold rolled and thermoplastically formed glassy alloys can be processed subsequent to the thermoplastic forming step to form parts. Such methods include punching portions from the glassy alloy, water jet cutting, laser cutting, slitter cutting, or any other method known in the art.
In some aspects, the method can be used to fabricate parts, such as leaf springs, that require a predictable material thickness. Glassy alloys are believed to deform easily. The viscosity of supercooled liquid of glassy alloys (e.g. Zr-based glassy alloys) is on the order of about 10⁶to 10⁷Pas, and the time for thermoplastic processing of such glassy alloys can be limited to below 1 minute. Without wishing to be held to a specific mode or theory of action, using conventional pressing methods to press a button glassy alloy into a 0.2 mm plate and 2 cm square with normal press strain rate (10²) would require a load of over 40 tons. A die used to compress such a material would be rendered unusable because the die would elastically deform. The deformed die subsequently would produce glassy alloy parts with non-uniform thicknesses. Methods that combine cold rolling and thermoplastic forming allow formation of glassy alloy structures such as leaf springs that have a predictable material thickness.
Other aspects of the disclosure relate to glassy alloy parts comprised of a glassy alloy formed from a combination of cold rolling and thermoplastic forming as described herein. In certain aspects, the glassy alloy part may have a variation in thickness of less than about 10%, less than about 8%, less than about 6%, less than about 5%, etc.
In other aspects, the glassy metal part may be substantially free of shear bands. Again, as used herein, substantially shear band-free glassy alloy can have less than 2% of the total surface area of the glassy alloy having shear bands. Alternatively, substantially shear band-free glassy alloy can have less than 1% of the total surface area of the glassy alloy having shear bands. Alternatively, substantially shear band-free glassy alloy can have less than 0.1% of the total surface area of the glassy alloy having shear bands. Alternatively, substantially shear band-free glassy alloy can have less than 0.01% of the total surface area of the glassy alloy having shear bands. Alternatively, substantially shear band-free glassy alloy can have no shear bands.
In a further aspect, the disclosure is further directed to methods of controlling the quality of a glassy alloy. Crystals are considered defects within a glassy alloy. In various embodiments, the glassy alloy is cold rolled at a temperature less than Tg of the alloy to form a flattened glassy alloy. The flattened glassy alloy is examined for the presence of cracks radiating from a particular point in the alloy. The presence of cracks radiating from a point in the alloy determines the presence of a crystal in the glassy alloy.
Any glassy alloy in the art may be used in the methods described herein. As used herein, the terms glassy alloy, metallic glass alloy, metallic glass-forming alloy, amorphous metal, amorphous alloy, bulk solidifying amorphous alloy, BMG alloy, and bulk metallic glass alloy are used interchangeably.
In various embodiments, the glassy alloy can be a nickel (Ni) based alloy, iron (Fe) based alloy, copper (Cu) based alloy, zinc (Zi) based alloy, zirconium (Zr) based alloy, gold (Au)-based alloy, platinum (Pt) based alloy, palladium (Pd) based alloy, or any other glassy alloy. Similarly, glassy alloy described herein as a constituent of a composition or glassy alloy part can be of any type. As recognized by those of skill in the art, glassy alloys may be selected based on and may have a variety of potentially useful properties. In particular, glassy alloys tend to be stronger than crystalline alloys of similar chemical composition.
The glassy alloy can comprise multiple transition metal elements, such as at least two, at least three, at least four, or more, transitional metal elements. The alloy can also optionally comprise one or more nonmetal elements, such as one, at least two, at least three, at least four, or more, nonmetal elements. A transition metal element can be any of scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, yttrium, zirconium, niobium, molybdenum, technetium, ruthenium, rhodium, palladium, silver, cadmium, hafnium, tantalum, tungsten, rhenium, osmium, iridium, platinum, gold, mercury, rutherfordium, dubnium, seaborgium, bohrium, hassium, meitnerium, ununnilium, unununium, and ununbium. In one embodiment, a BMG containing a transition metal element can have at least one of Sc, Y, La, Al, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Tc, Re, Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Zn, Cd, and Hg. Depending on the application, any suitable transitional metal elements, or their combinations, can be used.
Depending on the application, any suitable nonmetal elements, or their combinations, can be used. A nonmetal element can be any element that is found in Groups 13-17 in the Periodic Table. For example, a nonmetal element can be any one of F, Cl, Br, I, At, O, S, Se, Te, Po, N, P, As, Sb, Bi, C, Si, Ge, Sn, Pb, and B. Occasionally, a nonmetal element can also refer to certain metalloids (e.g., B, Si, Ge, As, Sb, Te, and Po) in Groups 13-17. In one embodiment, the nonmetal elements can include B, Si, C, P, or combinations thereof. Accordingly, for example, the alloy can comprise a boride, a carbide, or both.
In some embodiments, the glassy alloy composition described herein can be fully alloyed. The term fully alloyed used herein can account for minor variations within the error tolerance. For example, it can refer to at least 90% alloyed, such as at least 95% alloyed, such as at least 99% alloyed, such as at least 99.5% alloyed, such as at least 99.9% alloyed. The percentage herein can refer to either volume percent or weight percentage, depending on the context. These percentages can be balanced by impurities, which can be in terms of composition or phases that are not a part of the alloy. The alloys can be homogeneous or heterogeneous, e.g., in composition, distribution of elements, amorphicity/crystallinity, etc.
The glassy alloy can include any combination of the above elements in its chemical formula or chemical composition. The elements can be present at different weight or volume percentages. Alternatively, in one embodiment, the above-described percentages can be volume percentages, instead of weight percentages. Accordingly, a glassy alloy can be zirconium-based, titanium-based, platinum-based, palladium-based, gold-based, silver-based, copper-based, iron-based, nickel-based, aluminum-based, molybdenum-based, and the like. The glassy alloy can also be free of any of the aforementioned elements to suit a particular purpose. For example, in some embodiments, the glassy alloy, or the composition including the glassy alloy, can be substantially free of nickel, aluminum, titanium, beryllium, or combinations thereof. In one embodiment, the alloy or the composite is completely free of nickel, aluminum, titanium, beryllium, or combinations thereof.
The afore described glassy alloy systems can further include additional elements, such as additional transition metal elements, including Nb, Cr, V, and Co. The additional elements can be present at less than or equal to about 30 wt %, such as less than or equal to about 20 wt %, such as less than or equal to about 10 wt %, such as less than or equal to about 5 wt %. In one embodiment, the additional, optional element is at least one of cobalt, manganese, zirconium, tantalum, niobium, tungsten, yttrium, titanium, vanadium and hafnium to form carbides and further improve wear and corrosion resistance. Further optional elements may include phosphorous, germanium and arsenic, totaling up to about 2%, and preferably less than 1%, to reduce melting point. Otherwise incidental impurities should be less than about 2% and preferably 0.5%.
In some embodiments, a composition having a glassy alloy can include a small amount of impurities. The impurity elements can be intentionally added to modify the properties of the composition, such as improving the mechanical properties (e.g., hardness, strength, fracture mechanism, etc.) and/or improving the corrosion resistance. Alternatively, the impurities can be present as inevitable, incidental impurities, such as those obtained as a byproduct of processing and manufacturing. The impurities can be less than or equal to about 10 wt %, such as about 5 wt %, such as about 2 wt %, such as about 1 wt %, such as about 0.5 wt %, such as about 0.1 wt %. In some embodiments, these percentages can be volume percentages instead of weight percentages. In one embodiment, the glassy alloy sample/composition consists essentially of the glassy alloy (with only a small incidental amount of impurities). In another embodiment, the composition includes a glassy alloy (with no observable trace of impurities).
FIG. 2 shows a viscosity-temperature graph of an exemplary glassy alloy, from an exemplary series of Zr—Ti—Ni—Cu—Be alloys manufactured by Liquidmetal Technology. It should be noted that there is no clear liquid/solid transformation for a bulk solidifying amorphous metal during the formation of an amorphous solid. The molten alloy becomes more and more viscous with increasing undercooling until it approaches solid form around the glass transition temperature. Accordingly, the temperature of solidification front for bulk solidifying metallic glass-forming alloys can be around glass transition temperature, where the alloy will practically act as a solid for the purposes of pulling out the quenched amorphous sheet product.
FIG. 3 shows the time-temperature-transformation (TTT) cooling curve of an exemplary glassy alloy, or TTT diagram. Bulk-solidifying amorphous metals do not experience a liquid/solid crystallization transformation upon cooling, as with conventional metals. Instead, the highly fluid, non-crystalline form of the metal found at high temperatures (near a “melting temperature” Tm) becomes more viscous as the temperature is reduced (near to the glass transition temperature Tg), eventually taking on the outward physical properties of a conventional solid.
Even though there is no liquid/crystallization transformation for a bulk solidifying amorphous metal, a melting temperature Tm may be defined as the thermodynamic liquidus temperature of the corresponding crystalline phase. FIG. 3 shows processing methods of die casting from at or above Tm to below Tg without example time-temperature trajectory (1) hitting the TTT curve. Time-temperature trajectories (2), (3), and (4) depict processes at or below Tg being heated to temperatures below Tm. Under this regime, the viscosity of bulk-solidifying amorphous alloys at or above the melting temperature Tm could lie in the range of about 0.1 poise to about 10,000 poise, and even sometimes under 0.01 poise. A lower viscosity at the “melting temperature” would provide faster and complete filling of intricate portions of the shell/mold with a bulk solidifying amorphous metal for forming the metallic glass parts. Furthermore, the cooling rate of the molten metal to form a metallic glass part has to such that the time-temperature profile during cooling does not traverse through the nose-shaped region bounding the crystallized region in the TTT diagram of FIG. 3. In FIG. 3, Tnose (at the peak of crystallization region) is the critical crystallization temperature Tx where crystallization is most rapid and occurs in the shortest time scale.
The supercooled liquid region, the temperature region between Tg and Tx is a manifestation of the stability against crystallization of bulk solidification alloys. In this temperature region the bulk solidifying alloy can exist as a high viscous liquid. The viscosity of the bulk solidifying alloy in the supercooled liquid region can vary between 1012 Pa s at the glass transition temperature down to 105 Pa s at the crystallization temperature, the high temperature limit of the supercooled liquid region. Liquids with such viscosities can undergo substantial plastic strain under an applied pressure. The embodiments herein make use of the large plastic formability in the supercooled liquid region as a forming and separating method.
Technically, the nose-shaped curve shown in the TTT diagram describes Tx as a function of temperature and time. Thus, regardless of the trajectory that one takes while heating or cooling a metal alloy, when one hits the TTT curve, one has reached Tx. In FIG. 3, Tx is shown as a dashed line as Tx can vary from close to Tm to close to Tg.
The schematic TTT diagram of FIG. 3 shows processing methods of die casting from at or above Tm to below Tg without the time-temperature trajectory (shown as (1) as an example trajectory) hitting the TTT curve. During die casting, the forming takes place substantially simultaneously with fast cooling to avoid the trajectory hitting the TTT curve. The processing methods for superplastic forming (SPF) from at or below Tg to below Tm without the time-temperature trajectory (shown as (2), (3) and (4) as example trajectories) hitting the TTT curve. In SPF, the amorphous bulk metallic glass is reheated into the supercooled liquid region where the available processing window could be much larger than die casting, resulting in better controllability of the process. The SPF process does not require fast cooling to avoid crystallization during cooling. Also, as shown by example trajectories (2), (3) and (4), the SPF can be carried out with the highest temperature during SPF being above Tnose or below Tnose, up to about Tm. If one heats up a piece of metallic glass-forming alloy but manages to avoid hitting the TTT curve, you have heated “between Tg and Tm,” but one would have not reached Tx.
Typical differential scanning calorimeter (DSC) heating curves of bulk-solidifying metallic glass-forming alloys taken at a heating rate of 20 C/min describe, for the most part, a particular trajectory across the TTT data where one would likely see a Tg at a certain temperature, a Tx when the DSC heating ramp crosses the TTT crystallization onset, and eventually melting peaks when the same trajectory crosses the temperature range for melting. If one heats a bulk-solidifying metallic glass-forming alloy at a rapid heating rate as shown by the ramp up portion of trajectories (2), (3) and (4) in FIG. 4A, then one could avoid the TTT curve entirely, and the DSC data would show a glass transition but no Tx upon heating. Another way to think about it is trajectories (2), (3) and (4) can fall anywhere in temperature between the nose of the TTT curve (and even above it) and the Tg line, as long as it does not hit the crystallization curve. That just means that the horizontal plateau in trajectories might get much shorter as one increases the processing temperature.
The methods herein can be valuable in the fabrication of electronic devices using a glassy alloy. An electronic device herein can refer to any electronic device known in the art. For example, it can be a telephone, such as a cell phone, and a land-line phone, or any communication device, such as a smart phone, including, for example an iPhone®, and an electronic email sending/receiving device. It can be a part of a display, such as a digital display, a TV monitor, an electronic-book reader, a portable web-browser (e.g., iPad®), watch and a computer monitor. It can also be an entertainment device, including a portable DVD player, conventional DVD player, Blue-Ray disk player, video game console, music player, such as a portable music player (e.g., iPod®), etc. It can also be a part of a device that provides control, such as controlling the streaming of images, videos, sounds (e.g., Apple TV®), or it can be a remote control for an electronic device. It can be a part of a computer or its accessories, such as the hard drive tower housing or casing, laptop housing, laptop keyboard, laptop track pad, desktop keyboard, mouse, and speaker. The article can also be applied to a device such as a watch or a clock.
Any ranges cited herein are inclusive. The terms “substantially” and “about” used throughout this Specification are used to describe and account for small fluctuations. For example, they can refer to less than or equal to. ±5%, such as less than or equal to ±2%, such as less than or equal to ±1%, such as less than or equal to ±0.5%, such as less than or equal to ±0.2%, such as less than or equal to ±0.1%, such as less than or equal to ±0.05%.
The foregoing description, for purposes of explanation, used specific nomenclature to provide a thorough understanding of the described embodiments. However, it will be apparent to one skilled in the art that the specific details are not required in order to practice the described embodiments. Thus, the foregoing descriptions of the specific embodiments described herein are presented for purposes of illustration and description. They are not target to be exhaustive or to limit the embodiments to the precise forms disclosed. It will be apparent to one of ordinary skill in the art that many modifications and variations are possible in view of the above teachings.

EXAMPLES

The following non-limiting examples are provided to illustrate aspects of the disclosure.

Example 1

In an example to demonstrate the improved thickness control of the methods of the disclosure, comparative glassy alloys were prepared. First, it was demonstrated that thermoplastic forming alone does not provide for a reproducible and predictable thickness with high tolerance. FIG. 4A depicts the result of four separate attempts at forming a glassy alloy by thermoplastic forming to within a tolerance window of 0.20+/−0.02 mm. Three of the four samples were outside the tolerance range. FIG. 4B shows the thickness of a thermoplastic pressed plate. The thickness was non-uniform over the plate, measured to 0.28+/−0.09 mm (a variation of approximately 30%).
Using the methods of the present disclosure, it was shown that cold rolling allows for close control of the thickness of the glassy alloy feedstock to thermoplastic forming processing. FIG. 4C depicts cold rolled ribbon of glassy alloy. The cold rolled ribbon has a thickness of 0.22+/−0.02 mm over the surface. As such, glassy alloy parts that can be manufactured using the methods described herein can have predictable and reproducible thickness within 10% of the thickness value, or within 0.04 mm deviation of the part in FIG. 4B.

Example 2

In accordance with aspects of the present disclosure, glassy alloys that are formed by cold rolling followed by thermoplastic forming according to methods of the present disclosure provide structural relaxation that reduces or eliminates shear banding and micro-cracking without loss of glassy alloy strength.
Table 1 shows the yield strength of a 4 mm wide×2 mm thick Pt850 alloy when prepared as-cast and by cold rolling followed by thermoplastic forming according to the disclosure. The combination of cold-rolling and thermoplastic forming produced glassy alloys having higher hardness with greater bending deflection than the same as-cast glassy alloy. The yield strength of the cold-rolled/thermoplastic glassy alloy was above what would be expected by an as-cast system.

TABLE 1

Thermoplastic Deformation of Platinum Alloy at 270° C.

As-cast

Thermoplastic

Sample	σ_m(MPa)	δ_f(mm)	σ_m(MPa)	δ_f(mm)	time

1	2558	1.82	2377	1.63	90
2	2580	1.89	2482	1.74	60
3	2555	1.83	2459	1.60	60
4	2554	1.48	2578	1.96	30
5	2515	1.70	2496	1.96	30
Mean	2552 ± 23	1.74 ± 0.16	2478 ± 72	1.78 ± 0.17

FIG. 5 shows the bending deflection curves of as-cast glassy alloys compared to cold rolled/thermoplastic formed (TP) Pt850 alloys in a 3-points bending test to determine structural relaxation embrittlement. Of note, there is no significant degradation of fracture strain in TP samples at a thermoforming time of 30 s, thereby demonstrating no structural relaxation embrittlement of Pt-850 glassy alloy.
An example of punched Pt-850 glassy alloy part produce by a cold-rolling/thermoplastic forming method of the disclosure is shown in FIGS. 6A-C. FIG. 6A illustrates a cross-section of punched Pt-850 glassy alloy produced according to the methods of the disclosure, showing a smooth, flat shear fracture near the top surface, and a rough shear fracture near the bottom surface. Exploded views show that there is nearly no undercut (FIG. 6B) or burr (FIG. 6C) formed during punching.
As demonstrated, the structural properties of the glassy alloys produced according to the methods of the disclosure provide material that is excellent for shaping via machine processes such as punching. For instance, given the reproducibility of thickness and lack of structural relaxation embrittlement described herein, the glassy alloy materials produced according to the methods of the disclosure are particularly suited for shaping via machine processes such as punching.
While this disclosure has been described with reference to specific embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof, without departing from the spirit and scope of the disclosure. In addition, modifications may be made to adapt the teachings of the disclosure to particular situations and materials, without departing from the essential scope thereof. Thus, the disclosure is not limited to the particular examples that are disclosed herein, but encompasses all embodiments falling within the scope of the appended claims.

Claims

What is claimed:

1. A method of forming a glassy alloy comprising:

cold rolling a glassy alloy feedstock at a temperature less than the glass transition temperature (Tg) of the glassy alloy feedstock to form a flattened glassy alloy; and

thermoplastically forming the flattened glassy alloy at a temperature at or above Tg of the glassy alloy feedstock to form the glassy alloy.

2. The method of claim 1, wherein the glassy alloy has a thickness that does not vary by more than about 10% after cold rolling and thermoplastic forming.

3. The method of claim 1, wherein the flattened glassy alloy has a thickness that is within about 0.04 mm of the thickness of the glassy alloy.

4. The method of claim 1, wherein the flattened glass alloy comprises one or more shear bands.

5. The method of claim 4, wherein the thermoplastic forming heals the one or more shear bands in the flattened glassy alloy to form a substantially shear band-free glassy alloy.

6. The method of claim 5, wherein less than 2% of the total surface area of the substantially shear band-free glassy alloy comprises shear bands.

7. The method of claim 1, wherein the glassy alloy is selected from a nickel (Ni) based glassy alloy, an iron (Fe) based glassy alloy, a copper (Cu) based glassy alloy, a zinc (Zi) based glassy alloy, a zirconium (Zr) based glassy alloy, a gold (Au)-based glassy alloy, a platinum (Pt) based glassy alloy, and a palladium (Pd) based glassy alloy.

8. The method of claim 1, wherein the flattened glassy alloy is thermoplastically formed for 15 to 90 seconds.

9. The method of claim 1, wherein the glassy alloy is a Pt-based glassy alloy.

10. The method of claim 9, wherein the flattened glassy alloy is thermoplastically formed for 15 to 30 seconds.

11. A glassy alloy part comprised of a glassy alloy and formed from a combination of cold rolling and thermoplastic forming, wherein the glassy alloy part has a variation in thickness of less than about 10% and is substantially free of shear bands.

12. The glassy alloy part of claim 11, wherein less than 2% of the total surface area of the glassy alloy part comprises shear bands.

13. The glassy alloy part of claim 11, wherein the glassy alloy is selected from a nickel (Ni) based glassy alloy, an iron (Fe) based glassy alloy, a copper (Cu) based glassy alloy, a zinc (Zi) based glassy alloy, a zirconium (Zr) based glassy alloy, a gold (Au)-based glassy alloy, a platinum (Pt) based glassy alloy, and a palladium (Pd) based glassy alloy.

14. The glassy alloy part of claim 11, wherein the glassy alloy is a Pt-based glassy alloy.

15. The glass alloy part of claim 11, wherein the glass alloy part exhibits no structural relaxation embrittlement.

16. A method of determining the presence of a crystalline metal in a glassy alloy comprising:

cold rolling a glassy alloy feedstock at a temperature less than Tg of the glassy alloy to form a flattened glassy alloy; and

determining the presence of cracks radiating from a portion of the flattened glassy alloy, the portion of the flattened glassy alloy corresponding to the presence of the crystalline metal in the flattened glassy alloy.

17. The method of claim 16, wherein the glassy alloy is selected from a nickel (Ni) based glassy alloy, an iron (Fe) based glassy alloy, a copper (Cu) based glassy alloy, a zinc (Zi) based glassy alloy, a zirconium (Zr) based glassy alloy, a gold (Au)-based glassy alloy, a platinum (Pt) based glassy alloy, and a palladium (Pd) based glassy alloy.

18. The method of claim 16, further comprising thermoplastically forming the flattened glassy alloy at a temperature at or above Tg of the glassy alloy feedstock to form the glassy alloy.

19. The method of claim 16, wherein the glassy alloy has a thickness that does not vary by more than about 10% after cold rolling and thermoplastic forming.

20. The method of claim 19, wherein the thermoplastic forming heals cracks radiating from a portion of the flattened glassy alloy.